Remorhaz, how do YOU do the different ACs??

[garhkal]

So, we have around a handful of monsters in the MM whether 1e or 2e, such as the Fearsome Beholder, the always scary Remorhaz and the land-sharks the Bulletes, all of which have variable AC's depending on where one is hitting...

So how do YOU Handle it when pcs encounter one of those foes?
Is it based on where their minis are (like if they were fighting said remorhaz, if 3 minis are in the front while the rest are on the flank, those in front get to attack the underbelly if they win initiative, otherwise its just the head, while those on the flank only get the body)??
Do you ignore different AC for those critters and just give them ONE flat AC all over??